Re: [Linaro-acpi] [PATCH 2/2] ACPI / scan: Parse _CCA and setup device coherency

On Wednesday 29 April 2015 08:44:09 Suravee Suthikulpanit wrote:

•                   device->flags.cca_seen = 1;
  

•           } else if (IS_ENABLED(CONFIG_ACPI_MUST_HAVE_CCA)) {
  

•                   /*
  

•                    * Architecture has specified that if the device
  

•                    * can do DMA, it must have ACPI _CCA object.
  

•                    * Here, there could be two cases:
  

•                    *   1. Not DMA-able device.
  

•                    *   2. DMA-able device, but missing _CCA object.
  

•                    *
  

•                    * In both cases, we will default to dma non-coherent.
  

•                    */
  

•                   cca = 0;
  

•           } else {
  

•                   /*
  

•                    * If architecture does not specify that device must
  

•                    * specify ACPI _CCA (e.g. x86), we default to use
  

•                    * dma coherent.
  

•                    */
  

•                   cca = 1;
  

•           }
  
  

What does it mean here if a device does DMA but is not coherent? Do you have an example of a server that needs this?

Can we please make the default for ARM64 cca=1 as well?

Arnd